Armor Plate with Shock Wave Absorbing Properties

ABSTRACT

A composite armor plate includes a fracture layer placed adjacent to a ceramic layer. The ceramic layer provides a ballistic resistant layer that receives a ballistic impact and propagates a compression wave. The fracture layer is placed behind the ceramic layer and absorbs a portion of the compression wave propagating out in front of the ballistic impact. The absorbed compression wave causes the fracture layer to at least partially disintegrate into fine particles, which dissipates energy in the process. To cause a higher degree of fracturing (and thus larger dissipation of compression wave energy) the fracture layer includes a plurality of resonators embedded in a fracture material.

REFERENCE TO RELATED APPLICATION

This application is a divisional of, and claims priority to and thebenefits of, U.S. patent application Ser. No. 13/047,288 filed on Mar.14, 2011, the entirety of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates to armor plates and articles ofmanufacture incorporating the armor plates.

2. The Relevant Technology

Armor is a material or system of materials designed to protect fromballistic threats. Transparent armor, in addition to providingprotection from the ballistic threat is also designed to be opticallytransparent, which allows a person to see through the armor and/or toallow light to illuminate the area behind the armor.

In the general field of ballistic armors, existing armor systems aretypically comprised of many layers of projectile resistant materialseparated by polymer interlayers, which bond the projectile resistantmaterials. In a typical armor laminate the strike surface is a hardlayer of projectile resistant material that is designed to break up ordeform projectiles upon impact. The interlayer materials are used tomitigate the stresses from thermal expansion mismatches as well as tostop crack propagation into the polymers.

For most armor plates, efforts are usually made to make the armor platelight weight. This is particularly true of transparent armor plates,which are often used for protective visors and goggles. Currentlyexisting military specification for protective visors and gogglesrequires that the lens should be able to stop .22-caliber 17 grain FSPprojectile at 550-feet per second (fps). For comparison, most handgunsgive more than 1000 fps bullet velocity and rifles up to 3000 fps. Tostop bullets from handguns one needs an inch thick polycarbonate plateand around two inches thickness for a rifle bullet.

Accordingly, what is needed in the art are armor plates that haveimproved resistance to a projectile for a given weight and/or thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an armor plate according to one embodiment of theinvention and a projectile about to strike the surface of the armorplate;

FIG. 2 illustrates a fracture layer of the armor plate shown in FIG. 1having a plurality of resonator layers according to one embodiment ofthe invention;

FIG. 3 illustrates a fracture layer of the armor plate shown in FIG. 1having a plurality of spheroidal particulate resonators according to oneembodiment of the invention;

FIG. 4 illustrates a fracture layer of the armor plate shown in FIG. 1having a plurality of non-spheroidal particulate resonators according toone embodiment of the invention;

FIG. 5 is a graph showing the surface area of particles derived from 1cm³ of material as a function of particle size;

FIG. 6 is a graph showing fracture energy absorbed by 1 cm³ of glassfractured as a function of particle size at 11 km/s impact;

FIG. 7 illustrates a pressure sine wave at the 0.45 GHz spectral line ofsoda-lime glass;

FIG. 8 illustrates the armor plate of FIG. 1 showing the projectileafter impact;

FIG. 9 illustrates an armor plate with adjacent layers of materialjoined using an adhesive;

FIG. 10 illustrates an armored vehicle according to one embodiment ofthe invention incorporating the inventive armor plate;

FIG. 11 illustrates a helmet according to an alternative embodiment ofthe invention incorporating the inventive armor plate;

FIG. 12 illustrates a pair of goggles incorporating the inventive armorplate; and

FIG. 13 illustrates a panel including a plurality of segments of theinventive armor plate.

DETAILED DESCRIPTION

The present invention relates to a composite armor plates and articlesof manufacture incorporating the armor plate. The composite armor plateincludes a strike face layer adjacent a fracture layer, which is alsoplaced adjacent a ceramic layer. The ceramic layer provides a ballisticresistant layer that receives a ballistic impact and propagates acompression wave accumulated in the strike layer. The ceramic layerprovides toughness that impedes the projectile and may accelerate andspread out the compression wave. The fracture layer is placed behind theceramic layer and absorbs a portion of the compression wave propagatingout in front of the projectile mostly by the failure wave mechanism. Theabsorbed compression wave causes the fracture layer to at leastpartially disintegrate into fine particles, which absorbs energy in theprocess.

To cause a higher degree of fracturing (and thus larger absorption ofcompression wave energy) the fracture layer includes a plurality ofresonators embedded in a fracture material which work as seeds for thefailure wave. The resonators can be repeating thin layers of a resonatormaterial (i.e., alternating layers of fracture material and thin sheetsof resonator material). Or alternatively, the resonators can beparticles dispersed in the fracture material. The resonators have a sizeand composition that reflects and stores wave energy (i.e., acousticphonons) generated in the fracture layer.

The composition of the fracture material is selected to give high energyacoustic spectral line to intercept energy from a decomposingcompressive wave. The principles of resonance are implemented toincrease the life-time of the acoustic spectral line. The resonators areselected to have a thickness that is half the wavelength (λ) of theacoustic spectral line as measured using the sound velocity of theresonator material (described more fully below). Selecting a resonatorthickness of λ/2 and using a resonator material that has mechanicalproperties different than the fracture material creates an interfacecapable of reflecting the phonons, which sustains the phonons (waves)for a longer period of time. By sustaining the waves for a longer periodof time, the waves are able to fracture more of the fracture material,thereby dissipating more energy.

The intensity of the acoustic spectral line depends on the fracturematerial chosen. The acoustic spectral lines of the fracture materialare a property of the material itself. The wavelength of the acousticspectral lines is the same even if the compression wave changes so longas the compression wave has sufficient energy to activate vibrations ata particular acoustic spectral line wavelength. Since the acousticspectral line emissions have a fixed wavelength in a given material(i.e., a fixed frequency), the resonators can be specifically designedto cause resonance in a particular fracture material.

Materials that can absorb a high energy shock wave and generate waveenergy in an acoustic spectral line with a frequency suitable forenhancing fracturing include, but are not limited to amorphous materialssuch as glasses. Crystalline materials may be used so long as thematerial includes lattice asymmetries (i.e., materials other than cubiccrystalline materials and/or monocrystalline materials) and thecrystalline material has a tensile strength lower than the resonator.Examples include non-cubic crystalline materials such as, but notlimited to titania, alumina, and magnesium oxide.

The use of resonators in the fracture layer can increase the ballisticresistance of the armor plate and/or allow reduced thicknesses of thefracture layer needed to achieve a desired ballistic resistance. Armorplates including a fracture layer with resonators can be madecomparatively lighter, stronger, and/or thinner than armor materialsusing un-doped fracture layers and/or armor materials using conventionallaminates.

In one embodiment, the armor plate can be transparent. Transparent armorplates can be incorporated into windows, helmets, goggles, and similardevices where transparency and/or translucency are desired. In otherembodiments, the armor plate can include one or more layers that areopaque.

Optionally, the armor plates of the present invention can achieve aneven lighter, thinner armor by placing a deformable layer on the frontside of the ballistic-resistant ceramic layer. The use of a deformablelayer in front of the strong ceramic layer causes the shock wave tospread out before it strikes the ceramic layer. When the large surfacearea shock wave strikes the fracture layer, the larger surface arearesults in comparatively larger area of the fracture layer beingdisintegrated, which dissipates a comparatively larger amount of energy.Depending on the plate geometry, projectile size and speed, ordersof-magnitude increase in energy absorption can be achieved using afracture layer with resonators either alone or in combination with adeformable layer in front of the ceramic layer.

FIG. 1 illustrates an example armor plate 100 according to oneembodiment of the invention. The armor plate 100 includes an optionaltransparent deformable layer 110, a transparent ceramic layer 112, afracture layer 114, and an optional spall liner 116. While armor plate100 is described below as having a deformable layer 110 and a spallliner 116, those skilled in the art will recognize that the principlesof the invention can be carried out without these layers and that thearmor plate 100 can include any number of other layers so long as anyshock wave of sufficient energy is transferred to the fracture layer andcauses at least partial disintegration (i.e., powder formation) of thefracture material.

Armor plate 100 has a strike surface 117 upon which a projectile 118impinges. Projectile 118 can be a bullet, shrapnel, debris or any otheritem or structure that could hit against armor plate 100. Armor plate100 also includes a back surface 119 opposite the strike surface 117.Strike surface 117 is configured to receive the initial impact ofprojectile 118 and back surface 119 is configured to be the surfaceclosest to the object for which the armor plate 100 provides protection.For example, where armor plate 100 is used as a window in an armoredvehicle, strike surface 117 is positioned outside the vehicle and backsurface 119 communicates with the interior of the vehicle.

In one embodiment, the optional deformable layer 110 has a first side120 configured to be the strike surface 117 upon which projectile 118impinges. Deformable layer 110 may be configured to generate acompression wave from the impact of projectile 118. In one embodimentdeformable layer 110 comprises a material having an elongation beforefailure of at least 20%. Materials having an elongation before failureof at least 20% typically generate an intense compression wave uponballistic impact. In a more preferred embodiment, the deformable layermay include a material having an elongation before failure of at leastabout 50%, even more preferably at least about 100% or more. Examples ofsuitable transparent materials that can be used for the deformable layer110 include, but are not limited to, polycarbonate, polyurethanes,elastic acrylic polymers, and combinations of these. Examples ofnontransparent deformable materials that can be used include aluminum,titanium, and combinations of these. Other materials can also be used.

If present, deformable layer 110 may include a backside 122 that opposesfirst side 120. Backside 122 is adjacent ceramic layer 112. As will bediscussed below in greater detail, backside 122 may be adhered to orotherwise bonded directly to ceramic layer 112 or alternatively backside122 may be held in direct contact with ceramic layer 112 without beingbonded thereto, such as by mechanical connection. For example,deformable layer 110 and ceramic layer 112 can be adhered using a resinsuch as, but not limited to, poly(vinylbutiral) or secured together byfixing the layers within a frame and/or clamping.

The thickness of deformable layer 110 may be selected to enhance thegeneration of the compression wave. In one embodiment the deformablelayer 110 has a thickness extending between faces 120 and 122 in a rangefrom about 0.5 mm to about 10 mm, more preferably about 1 mm to about 4mm. Opposing faces 120 and 122 can be disposed in parallel alignment sothat the thickness is constant. Alternatively, one or both of the facescan be angled relative to each other so that the thickness variesbetween faces 120 and 122. Faces 120 and 122 can also be contoured, suchas curved, so that they are not planar.

In one embodiment, deformable layer 110 is a single layer of ahomogeneous material. However, in some embodiments the deformable layer110 may be made from a plurality of sub-layers that together are highlydeformable (e.g., the sub-layers together have an elongation beforefailure of at least about 20%).

Ceramic layer 112 is positioned adjacent to and between deformable layer110 and fracture layer 114. Ceramic layer 112 has a front side surface124 and an opposing backside surface 128. Backside surface 128 isadjacent fracture layer 114. Ceramic layer 112 can be adhered to orotherwise bonded or secured to fracture layer 114 using the same methodsas previously discussed for securing ceramic layer 112 and deformablelayer 110.

Ceramic layer 112 is made from a strong, ballistic-resistant ceramicmaterial having a high sound velocity. The ceramic material willtypically have a sound velocity in a range from about 2-19 km/s, morespecifically 4-19 km/s, or even more specifically 8-19 km/s. Ceramiclayer 112 may also be transparent. Examples of suitable transparentceramic materials include sapphire, aluminum oxinitride (AlON), spinel,AlN, alumina, and combinations of these. Nontransparent ceramicmaterials can also be used. Examples of nontransparent ceramic materialsinclude, but are not limited to, silicon carbide, boronitride, boroncarbide, diamond, and combinations of these. These materials and similarmaterials with a high sound velocity are advantageous for allowing thecompression wave generated in the deformable layer 110 to spread out asit travels through ceramic layer 112 and for providing toughness in athin layer.

The thickness 132 of ceramic layer 112 extending between faces 124 and128 is typically selected to provide maximum strength while minimizingweight. Ceramics such as sapphire, aluminum oxynitride (AlON), andspinels typically need to have a minimal thickness before they willoutperform plastic materials (e.g., about 0.25 mm). After this minimalthickness, ceramics tend to provide better protection than plastics, butwith increased weight, as the density of transparent ceramics are 2 to 3times higher than the density of plastics. Thus, even where cost is notan issue, practical weight restrictions in some cases can limit thethickness of ceramic layer 112.

Even when relatively thick ceramic layers can be used, a thick ceramiclayer tends to transfer impact velocity to the substrate (e.g., theframes of protective eyewear), which may not be able to handle increasedforces and the whole system must be strengthened, again with weightincrease. Thus in some embodiments of the invention it is desirable tominimize the thickness of the ceramic layer 112. In one embodiment, thethickness may be less than 10 mm, more preferably less than about 6 mm,even more preferably less than about 4 mm, and most preferably less thanabout 2 mm. In one embodiment the thickness 132 can be in a range fromabout 0.5 mm to about 6 mm, more preferably about 0.8 mm to about 4 mm,and most preferably from about 1 mm to about 2 mm.

In one embodiment of the invention ceramic layer 112 may be a continuousand/or homogeneous layer of the ceramic material. However in analternative embodiment ceramic layer 112 may include a plurality ofsub-layers of the ceramic material. The sub-layers may be the same ordifferent ceramic materials and may be bonded or adhered together asdiscussed herein with respect to the connection between deformable layer110 and ceramic layer 112.

Fracture layer 114 is adjacent to and between ceramic layer 112 andoptional spall liner 116. Fracture layer 114 has a front side 130 and anopposing backside 134. Backside 134 may be adhered to or bonded to afront surface 136 of spall liner 116 in any manner similar to theconnection between deformable layer 110 and ceramic layer 112 asdiscussed above.

Fracture layer 114 is configured to receive a compression wave fromceramic layer 112 and at least partially disintegrate. Fracture layer114 includes a fracture material (e.g., glass or a brittle polymericmaterial) and a plurality of resonators (e.g., layers or particles oftitania). The thickness of fracture layer 114 can be selected to provideadequate volume for absorbing a compression wave generated in deformablelayer 110. The thickness 138 of fracture layer 114 extending betweenfaces 130 and 134 can be in a range from about 0.5 mm to about 10 mm,more specifically about 1 mm to about 5 mm. It is appreciated that allof the thicknesses discussed herein can also be considered to be interms of an average thickness, a maximum thickness, or a minimumthickness.

Fracture layer 114 is backed by spall liner 116 to stop (i.e. catch) thefractured particles of fractured layer 114. Spall liner 116 has a frontsurface 136 that is adjacent fracture layer 114. In one embodiment, aback surface 140 of spall liner 116 is configured to be the back surface119 of armor plate 110.

When a projectile strikes armor plate 100 and fracture layer 114 is atleast partially pulverized, the disintegrated particles will be small,but can still carry residual momentum. Spall liner 116 is made from amaterial capable of capturing the fine particles generated from fracturelayer 114. In one embodiment spall liner 116 may have relatively highelasticity such that spall liner 116 can expand to absorb the momentumof the fractured particles without rupturing.

Examples of suitable materials that can be used to make spall liner 116include polymers such as polycarbonate and polyurethane; woven ballisticfibers including para-aramids (e.g., Kevlar), ultra-high strengthpolyethylene fiber (e.g., Spectra and Dyneema),poly(p-phenylene-2,6-benzobisoxazole) (PBO), and/or boron fibers; andcombinations of these. In one embodiment, spall liner 116 can be madefrom a transparent material such as polycarbonate or Dynema.Alternatively, spall liner 116 can be nontransparent.

The thickness of spall liner 116 is selected to ensure sufficientstrength to withstand the residual momentum of the fractured particlesfrom fracture layer 114. Typically the thickness of spall liner 116 maybe in a range from about 0.5 mm to about 10 mm, more specificallybetween about 1 mm and 4 mm.

With reference to FIGS. 2-4, the fracture layer 114 is described infurther detail. FIGS. 2-4 illustrate various configurations of fracturematerial and resonators suitable for sustaining high energy waves. Withreference to FIG. 2, a fracture layer 114 a includes a plurality offracture material layers 170 a-170 c (collectively “fracture materiallayers 170”) that alternate between a plurality of resonator layers 172a-172 c (collectively “resonator layers 172”). The fracture materiallayers 170 are comprised of a fracture material 176 that is configuredto be pulverized upon ballistic impact.

FIGS. 3 and 4 illustrate alternative embodiments in which fracture layer114 includes particulate resonators. FIG. 3 shows a fracture layer 114 bthat includes spheroidal particulate resonators 178 a dispersed infracture material 176. FIG. 4 illustrates a fracture layer 114 c thatincludes fiber resonators 178 b dispersed in fracture material 176.

In the embodiments shown in FIGS. 2-4, the resonators 178 are embeddedin fracture material 176. Fracture material 176 is selected to have alower impact resistance or tensile strength than the material of ceramiclayer 112. To achieve high energy absorption by fracture layer 114, arelatively large volume of fracture material 176 is fractured into fineparticles. The absorbed energy increases with a decrease in the diameterof the fractured particle size due to an increase in surface area. FIG.5 is a graph showing the surface area of particles derived from 1 cm³ ofmaterial as a function of the particle size. As shown in FIG. 5, surfacearea increases exponential with decrease in particle size. Consequentlythe energy dissipated by fracture layer 114 increases exponentially withdecreases in particle size.

FIG. 6 shows the energy absorbed by 1 cm³ of glass fractured at 11 km/simpact. To illustrate the potential energy absorption of fracturedglass, the energy of an AK-47 bullet is plotted on the graph of FIG. 6.As shown in FIG. 6, 1 cm³ of glass is, in principle, capable ofabsorbing all the energy from a rifle bullet if the fractured grain sizeis smaller than about 1×10⁻⁷. The armor plate 100 of the presentinvention provides for substantial energy absorption in fracture layer114 by using resonators that sustain high energy waves capable offracturing the fracture material to finer particle sizes.

The resonators have a thickness that is selected to reflect waves withsufficient energy and life times to resonate in the fracture layer andpulverize the fracture material. Consequently, the fracture material isselected to generate wave energy of a desired frequency and theresonators are designed to resonate at that frequency. Thus, the designof the fracture layer generally includes selecting a proper fracturematerial to generate the desired wave frequency and properly configuringthe resonator to sustain that wave energy (thereby causing enhancedfracturing).

There exists a relationship between the frequency of the waves beingresonated and the size of the fractured particles. In general, higherenergy waves can cause finer fracturing of the fracture material. Thefrequency of wave that can fracture the brittle material to the desiredparticle sizes is typically greater than 100 MHz, more preferably 1 GHz,even more preferably, more than 10 GHz.

However, higher frequency phonons are also shorter lived. Theattenuation coefficient of a phonon is proportional to the square of thefrequency (α=α_(o)ν²). The corresponding intensity loss over distance xis: I=I_(o)e^(−αx). Since the coefficient is dependent on the square ofthe frequency and the intensity loss is a power of the attenuationcoefficient, phonon lifetimes can be very small for high frequencies.For example, a phonon lifetime for a phonon at 10 THz is ˜1 ps. Suchphonons are so short lived that it can be difficult to resonate suchparticles over a reasonable distance of the fracture material. Thus, thefracture material can be selected to produce waves having a frequencyless than 1 THz, more preferably less than 100 GHz and most preferablyless than 50 GHz.

Moreover, the density of states for most solids drops dramatically below1 meV (v˜1 THz). Thus, energy decaying from higher energy states tendsto form acoustic spectral lines with energy states concentrated inwell-defined narrow energy bands (e.g., in the 1-100 GHz range). Theseacoustic spectral lines are the result of the composition of thefracture material, which forbids broad based energy transfers across the1-100 GHz range. Thus, when designing resonators, targeting an acousticspectral line in the 1-100 GHz range can be advantageous because theresonators can pump a more concentrated energy band and thus cause amore intense fracturing, while minimizing the number of resonatorsneeded.

The resonating high energy waves have a reduced probability of decayinginto lower energy waves. Thus, a substantial portion of the decayingultra-high energy waves are pumped at the desired acoustic spectral linefrequency until they are dissipated by fracturing the fracture materialinto the desired small particles.

For many materials, the acoustic spectral lines in the 100 MHz-100 GHzare known. For example, soda-lime glass has acoustic spectral lines at450 MHz, 14 GHz, and 24 GHz. However, those skilled in the art willrecognize that the acoustic spectral lines for any suitable material canbe determined using Brillouin spectroscopy and/or using calculationsknown in the art.

Fracture materials that have acoustic spectral lines in the 100 MHz-100GHz range (and in particular the 1 GHz-50 GHz range) include amorphousmaterials such as glasses or crystalline materials with asymmetry, suchas non-cubic crystalline materials. Table 1 below provides a list ofexample glass-based fracture materials and a high energy spectral lineassociated therewith. However, the invention is not limited to thematerials listed in Table 1.

TABLE 1 Sound Velocity (km/s) Material C_(T) C_(L) f (GHz) SiO₂(vitreous quartz) 3.79 5.92 34.7 Borosilicate crown (wt. %: 71 SiO₂,3.29 5.49 33.2 14 B₂O₃, 10 Na₂O, 5 Al₂O₃) Borosilicate crown (wt. %:69.6 3.65 6.05 37.0 SiO₂, 9.9 B₂O₃, 8.4 Na₂O, 8.4 K₂O, 2.5 BaO) Silicateglass undoped (mol %: 60 3.83 6.59 41.1 SiO₂, 27.5 Li₂O₃, 10 CaO, 2.5Al₂O₃) Alkali-lead-silicate glass (wt %: . . . 3.49 25.8 27.3 SiO₂, 1.5K₂O, 71.0 PbO Dense lanthanum flint 3.56 5.55 43.0 Tantalum flint 3.215.99 43.7 Doped Phosphate glass with 0.3 wt 3.12 5.40 33.5 % Nd DopedPhosphate glass with 4.8 wt 3.13 5.49 33.9 % Nd2O₃ Doped fluorophophateglass 2.99 5.34 31.7 (mol %: 16% Al(PO₃)₃, 50% LiF, 33% NaF, 1% Nd₂O₃)

The fracture material is also selected to have a low fracture toughnessand high surface energy, which will maximize fracture absorption energy,typically at the expense of impact resistance. Typically, a lowerfracture threshold will give better energy absorption and less momentumtransfer to the armor plate supporting structure. For example regularsoda-lime or borosilicate glasses work better than tempered glass forthis application. The fracture material is also selected for its abilityto absorb high energy compression waves that will degrade into thephonons of the desired acoustic spectral line. One example of a suitablematerial that can be used as the fracture material is glass. As usedherein, the term “glass” is broadly intended to cover amorphous glass,soda glass, transparent silicates, alumina silicate, lithium aluminasilicate, borosilicate glass, alkali-lead-silicate, flints, phosphateglasses, cordierite glasses, fluorophosphates glass, doped glasses,combinations of the foregoing, and other known glasses. Other materialscan also be used, including but not limited to brittle polymericmaterials. For example, polymers having a elongation at break of lessthan 5% are brittle polymeric materials that can be used. The fracturematerial 176 may also be non-transparent. Examples of nontransparentmaterials include nontransparent silicates. Within a given glass type,absorbed fracture energy can be manipulated, if needed, by tempering theglass.

Upon being fractured, the fracture material will form particles thathave a particle size that correlates with the acoustic spectral lines ofthe material. Surprisingly, it has been found that the diameter of thefractured particles (caused by a ballistic impact) can have particlesizes that are similar to the wavelength of the acoustic spectral lineenergy. The wavelength of the acoustic spectral line can be determinedusing the equation λ_(i)=C_(i)/ν_(o) where λ_(i) is the wavelength inthe fracture material, C_(i) is the speed of sound in the material, andν_(o) is the frequency of the acoustic spectral line. For amorphousmaterials or crystalline materials with submicron grain sizes, there maybe two speeds of sound: longitudinal (C_(L)) and transversal (C_(T)).Table 2 below shows experimental peaks of a distribution of particlesfrom a soda-lime glass that was fractured by ballistic impact. The sodaglass has acoustic spectral lines at 0.45 GHz, 14 GHz and 24 GHz and alongitudinal sound velocity of 5100 m/s and a transversal sound velocityof 3200 m/s. The second line of Table 2 shows the calculated wavelengthof the acoustic spectral lines for both longitudinal and transversalsound velocities. The third row of Table 2 shows the peaks of theparticle size distribution of the fractured glass as measured usinglaser diffraction.

TABLE 2 ν, (GHz) 24 14 0.45 Calculated 133 213 228 365 7060 11400 λ,(nm) [C_(L)] [C_(T)] [C_(L)] [C_(T)] [C_(L)] [C_(T)] Experimental 129222 222 379 7000 11000 Peaks (nm)

As shown in Table 2, the experimentally determined peaks of the particlesizes of the fractured material are strikingly similar to the calculatedwavelength of the acoustic spectral lines. This demonstrates that wavepressure at the acoustic spectral lines in the 100 MHz to 100 GHz rangecan fracture the material.

Because smaller fracture sizes result in increased energy absorption, itis generally desirable to cause fracturing by acoustic spectral lineswith smaller wavelengths (i.e., higher frequencies). For example, moreenergy is dissipated by particles fractured by energy at the 24 GHzspectral line than the 450 MHz spectral line. However, depending on thecost and/or design of the resonator, it may be more desirable to targetacoustic spectral lines with somewhat shorter wavelengths.

After selecting the particular fracture material and determining thefrequency (i.e., the wavelength) of the acoustic spectral line to betargeted, the resonator can be designed and/or selected to sustain theacoustic spectral line intensity. Where mode dissipation in a resonatoris smaller, the mode lives longer before it decays into lower frequencymodes, thereby pumping energy into the desired acoustic spectral line ofthe surrounding material. When the amplitude of the acoustic spectralline pressure reaches the tensile strength of the fracture material, thefracture material will yield and fracture. The effects of amplitude areillustrated in FIG. 7, which show the 0.45 GHz spectral line ofsoda-lime glass. FIG. 7 shows the peaks reaching an amplitude (120 MPa)that can fracture glass within a period on the order of the wavelength.

The frequency of the acoustic spectral line may be used to determine thethickness of the resonators. The thickness of the resonators (i.e., thedistance between the reflecting surfaces of the resonator) may be adistance L defined by the formula: L=nλ/2, where n is an integer greaterthan or equal to one and λ is the wavelength of the acoustic spectralline in the resonator material.

The wavelength of the acoustic spectral line in the resonator may bedifferent than the wavelength in the fracture material. However, thefrequency is generally the same. Moreover, the wavelength can becalculated, as mentioned above, using the equation λ_(i)=C_(i)/ν_(o),where ν_(o) is the frequency of the acoustic spectral line in theresonator material and C_(i) is the speed of sound in the resonatormaterial.

The desired thickness of the resonator is defined by the longitudinalmodes. As is known in the art of resonance, resonant longitudinal modesare separated by frequency, where Δν=C/2πL or length Δλ=λ²/2πL. For abroadband resonator, L should be as small as possible. In oneembodiment, n is no greater than 4, no greater than 3, no greater than2, and most preferably n is 1. In most cases, achieving a resonator witha thickness that is exactly the same as the calculated thickness basedon wavelength (i.e., nλ/2) of the spectral line may be difficult.However, in the distribution of particles not all the particles must beat the desired thickness for the fracturing effect to be achieved.

For purposes of this invention, determining whether a distribution ofparticulate resonators has the desired particle size, the distributionof particulate resonators should include at least 5 mass % within aquarter wavelength at the spectral line frequency. Preferably at least25 mass %, more preferably at least 50 mass % and most preferably atleast 75 mass % of the distribution of resonator particles have a sizethat is less than λ/4 from the nλ/2 of the spectral line energy in theresonator material. Generally good levels of resonance can be achievedwhere at least 25%, preferably at least 50%, or at least 75% by mass ofthe resonators have a diameter that is less than λ/4, preferably lessthan λ/7, and most preferably less than λ/10 from the nλ/2 of thespectral line energy (i.e., the diameter of the desired percentage ofparticles of the particle distribution deviates no more than λ/4, etc.in the dimension targeting the desired λ).

The resonator material is selected to be a different material than thefracture material. In one embodiment, the resonator material is tougheror has a higher tensile strength than the fracture material to preventhigh energy waves from fracturing the resonator. The resonators may betransparent or non-transparent. Examples of suitable materials for theresonators include, but are not limited to refractory oxides, carbides,nitrides, or borides. Specific examples include, but are not limited toAl₂O₃, TiO₂, ZrO₂, MgO, AlN, TiN, ZrN, Si₃N₄, BN, SiC, TiC, WC, TiC,ZrC, TiB₂, diamond and the like, and combinations of these.

With reference again to FIG. 2, the resonator layers 172 can have athickness 174 that is nλ/2, where n is 1, 2, 3 or 4. The thickness offracture material layers 170 can be any thickness, although in apreferred embodiment, fracture material layers 170 also have a thicknessof nλ/2.

The thickness of fracture material layers 170 is preferably thicker thanthe thickness of resonator layers 172, such that the percentage ofresonator material within the fracture layer is substantially less thanthe percentage of fracture material. In one embodiment, the weightpercent of resonator material in fracture layer 114 a is less than 10 wt%, more preferably less than 5 wt %, and most preferably less than 1 wt%. The fracture layer can have any number of alternating fracturematerial layers 170 and resonator layers 172 to achieve a desiredthickness and potential for energy dissipation.

As discussed above, the resonators can be a particulate dispersed in thefracture material. FIG. 3 shows spheroidal particles 178 a dispersed ina fracture material 176 and FIG. 4 shows fiber particulates 178 bdispersed in fracture material 176 (collectively particulates arereferred to as “particulate resonators 178”). The particulate resonators178 typically have a thickness, which can correspond to the diameter, ofabout nλ/2. The particulate resonators 178 do not have to have all theirsurfaces at a distance of nλ/2, so long as the distance between at leasttwo reflecting surfaces of the particulate resonators is about nλ/2.

Particulate resonators 178 can be tubular, rectangular, spheroidal,multi-faceted, and/or regularly or irregularly shaped. Spheroidalparticulate resonators include particles that are generally globular inshape (e.g., the length and the width of the particles differ by lessthan a factor of 1.5). The particulate resonators can be nanoparticles,nanofibers, and/or similar structures made from material including, butnot limited to, Al₂O₃, TiO₂, ZrO₂, MgO, AlN, TiN, ZrN, Si₃N₄, BN, SiC,TiC, WC, TiC, ZrC, TiB₂, and the like, and combinations of these.

The size of the particulate resonators 178 (in the dimensioncorresponding to λ) may be in a range from 5 nm to 100 microns,preferably 10 nm to 50 microns, more preferably 20 nm to 10 microns, andmost preferably 40 nm to 1000 nm.

The concentration of the particulate resonators 178 (in the fracturelayer is selected to maximize resonance and energy dissipation whileminimizing cost. As the number of particulate resonators in the fracturematerial increases, the energy dissipation generally increases. However,as the concentration of particulate resonators increases, the amount offracture material and the probability that a resonator will be exposedto the proper wavelength of energy decreases. Thus, there can be adiminishing return on increasing the concentration of particulateresonators beyond a certain point. In one embodiment, the concentrationof the particulate resonators in the fracture material can be in a rangefrom 0.001 vol % to 10 vol %, more specifically 0.015 vol % to 5 vol %,and even more specifically from 0.01 vol % to 1.0 vol %.

The present invention also relates to methods for making armor platesthat include a fracture layer including resonators. In one embodimentthe method includes selecting a suitable fracture material having aspectrum line in a range from 100 MHz-100 GHz, preferably 1 GHz-50 GHzand forming a melt of the fracture material. The melt may be formed byheating the fracture material to a temperature that allows the fracturematerial to be mixed with a plurality of particulate resonators. Theparticulate resonators may be any of the particle shapes describedherein.

The particulate resonators can be incorporated by mixing or blending andmay optionally include the use of a solvent such as water or an organicsolvent. Organic solvents can be used to incorporate a resonator into abrittle polymeric fracture material.

In one embodiment, the particulate resonators may be dispersed in themelt and then the melt is allowed and/or caused to harden. For example,where amorphous glass is used as the fracture material, the molten glassmay be mixed with a metallic particulate resonators and then quenched tocool to a temperature below the glass transition temperature. To preventmelting of the particulate resonators, in one embodiment the particulateresonators can have a melt temperature that is higher than the melttemperature of the fracture material.

The fracture layers manufactured according to this embodiment can bejoined to the ceramic layer and/or other layers according to methodsknown in the art and/or described herein. For example, the fracturelayer 114 may be joined to the ceramic layer 112 using curable resins,heat, adhesives, pressure and/or mechanical connection. In analternative embodiment, the fracture material having the particulateresonators dispersed therein can be applied to the ceramic layer whilethe fracture material is still in a molten state. For example, themolten material can be poured, molded, injected or extruded onto or withthe ceramic layer. The fracture layer can then be allowed to cool.

FIG. 8 illustrates how armor plate 100 dissipates momentum fromprojectile 118. FIG. 8 shows projectile 118 penetrating front surface117 of armor plate 100. At the initial phase of a ballistic impactdeformable layer 110 deforms, creating the equivalent of localcompression. The compression wave then spreads out at a velocity closeto the speed of sound in ceramic layer 112. As projectile 118 movesthrough ceramic layer 112 it generates a lattice wave by movingdislocations, thereby transforming an additional portion of theprojectile energy into acoustic waves. The intensity ratio of thecompression wave to the lattice waves generated by moving dislocationsdepends on the thickness of the deformable layer 110 and ceramic layer112 relative to the projectile diameter and the properties of thematerials used for deformable layer 110 and ceramic layer 112.

One approach taken in making body armor relies on the theory that movingdislocations can last for a relatively long time, thereby spreadingtotal wave generation over time and making the impact less intense. Inreality this scenario is difficult to achieve, as deformation needed toabsorb significant energy typically is outside of acceptable armor platethickness for most applications. Hard ceramic plates efficiently convertimpact energy into the compression wave. This compression wave fracturesa portion of the ceramic, absorbing energy. High impact strength of theceramics results in the energy absorption in a fixed volume. As aresult, thin ceramics do not work well. Also, only a strong wave canfracture ceramics. Lower intensity waves go unaffected, contributing tothe momentum transfer to the substrate, which is especially undesirablefor a wearable armor.

In contrast, the proposed invention takes a counterintuitive approach.Armor plate 100 can include a soft material in front of ceramic layer112 (i.e., deformable layer 110). Instead of mitigating a shock wave,deformable layer 110 and ceramic layer 112 are amplifying the shockwave. As a projectile moves through deformable layer 110, pressure onceramic layer 112 builds up, effectively accumulating the compressionwave. Lattice wave generation also lasts longer.

The speed of sound in deformable layer 110 may be selected to berelatively small. When the compression wave reaches ceramic layer 112,for example sapphire, it accelerates to the speed of sound (e.g., from 3km/s to 11 km/s), thus becoming more intense. The compression wave alsospreads out. When the compression waves hits the fracture layer 114 itis close in intensity to the impact point, but can be spread out over anarea two orders of magnitude larger than the projectile cross-sectionarea.

When the compression wave strikes the fracture layer 114, acousticspectral line energy is generated and sustained to cause fine particlesto be created and energy dissipated as discussed above.

With reference now to FIG. 8, deformable layer 110, ceramic layer 112,fracture layer 114, and spall liner 116 can be joined together to formarmor plate 100 using any technique known in the art. In one embodiment,the layers of armor plate 100 are joined together using curable resins,heat, adhesives, and/or pressure. Preferably, the layers are secured toeach other such that armor plate 100 is at least translucent andpreferably transparent. In one embodiment transmission values of lightin the visible spectrum is at least about 70%, more preferably at leastabout 80%, and even more preferably at least about 90%.

FIG. 9 illustrates an example embodiment of armor plate 100 wheredeformable layer 110, ceramic layer 112, fracture layer 114, and spallliner 116 are joined together by a plurality of intermediate layers suchas adhesive layers 142 a, 142 b, and 142 c. Adhesive layers 142 a, 142b, and 142 c can be made from any material compatible with deformablelayer 110, ceramic layer 112, fracture layer 114, and/or spall liner116. Examples of suitable materials include polymers or resins such as,but not limited to, polyvinyl butyral, cyanoacrylates, epoxies,polyurethanes, acrylics, and combinations of these. The adhesives may betransparent or nontransparent. Other intermediate layers can also beapplied. In one embodiment intermediate layers such as, but not limitedto adhesive layers 142, may have a thickness less than 10 mm, morespecifically less than about 2 mm, more specifically less than about 1mm, or even less than 100 t. If present, the intermediate layers have athickness that does not prevent a compression wave from travelingbetween deformable layer 110, ceramic layer 112, and/or fracture layer114. For many materials, a thickness less than 2 mm more preferably lessthan 1 mm can be used.

The layers of armor plate 100 can also be held together in parallelusing means other than an adhesive. For example, armor plate 100 canhave deformable layer 110, ceramic layer 112, and/or fracture layer 114in free contact with one another, but clamped together using a frame orother clamping mechanism. A frame or other substrate, such as thoseillustrated in the devices shown in FIGS. 10-13, can apply a positiveforce on armor plate 110 to clamp or otherwise secured the layerstogether.

The overall thickness of armor plate 100 will typically depend on theamount of protection desired. Armor plates for preventing thepenetration of high momentum projectiles may be of greater thicknessthan those for preventing the penetration of lower momentum projectiles,but with increased weight. In one embodiment the combined thickness ofthe deformable layer, ceramic layer, fracture layer, and spall linerhave a thickness of less than 50 mm, more preferably less than 25 mm,even more preferably less than 20 mm, and most preferably less than 15mm. In an alternative embodiment, the deformable layer, the ceramiclayer, the fracture layer, and the spall liner have a combined thicknessin a range from about 4 mm to about 25 mm, more preferably from about 5mm to about 20 mm, and most preferably about 6 mm to about 15 mm. Thecombined thickness can be approximately the same or thinner than theprojectile size. For example the thickness can be 12.7 mm or less.

In some embodiments it may be desirable to make armor plate 100 as thinand as light as possible while achieving a desired level of protectionfrom projectile impact. To achieve a desired thinness, it can beadvantageous to make armor plate 100 with only four layers (i.e.,deformable layer, ceramic layer, fracture layer, and spall liner) andoptionally an adhesive between one or more of the layers and/or asurface coating for modifying optical transmissions (e.g., a tint).

In one embodiment, armor plate 100 may include additional layers onfront surface 117 and/or back surface 119. For example, armor plate 100may include coatings that modify the color and/or light transmissionthrough armor plate 100. In one embodiment a tint coating may be appliedto armor plate 100. For example, a tint coating may be desirable for anarmor plate used as a window to reduce the amount of light enteringthrough the window and/or to inhibit people on an outside of the windowto see inside.

To form armor plate 100, the layers of armor plate 100 can betemporarily fastened together, for example, with tape, and then placedin an autoclave, optionally under vacuum. The armor plate 100 may bepressurized and/or heated. Pressures that may be used includeatmospheric, greater than atmospheric, greater than 2 bar, greater than4 bar or greater than 8 bar. In some embodiments, pressure may beapplied in a pressure chamber or by mechanical means, for instance,rollers or a press. Pressure and heat may be applied until the adhesivelayers 142 (e.g., PVB) reach a softening point, allowing air bubbles tobe expelled and allowing the adhesive to clarify and flow.

The softening temperature of adhesives layers 142 may be, for example,greater than 70° C., greater than 100° C., greater than 150° C., greaterthan 200° C., or greater than 250° C. In some embodiments the optimumtemperature will depend on the pressure applied and the specificadhesive material used to bind the layers. In an alternative embodimentadhesive layers 142 can be polymerized to join the layers of armor plate100.

After hardening, cooling, and/or polymerizing, the layers of armor plate100 are securely immobilized in relation to each other and may bemounted in a substrate. FIGS. 10-13 illustrate example supportingstructures that armor plate 100 can be incorporated into. FIG. 10 showsan armored vehicle 150 having a first armor plate 100 a, a second armorplate 100 b, and a third armor plate 103 which function as windows onvehicle 150. Armor plates 100 a and 100 b are mounted in doors 152 and154, respectively of a body 156. Armor plate 100 c functions as a frontwindow. Body 156 provides a protective enclosure within its interior.Armor plates 100 a and 100 b may be transparent so as to allow personnelin the interior of body 156 the ability to view the surroundingsexterior to body 156. Body 156 may be made from an armored material,which is typically opaque. Armored vehicle 150 can include wheels 158 anengine cabin 160 and other features typical of vehicles for providinglocomotion (e.g., engine and drivetrain). Armored vehicle 150 can be ofany type known in the art, including but not limited to, cars, trucks,boats, airplanes, trains, and the like.

FIG. 11 illustrates a helmet 200 that incorporates an armor plate 100 daccording to the present invention. Armor plate 100 d is incorporatedinto a visor 202 having a curved surface secured to a helmet structure204 through a pair of fasteners 206 on opposing sides of helmetstructure 204. Visor 202 functions as a transparent face shield. Helmet200 may include one or more brackets 208 and 210 to support visor 202.Visor 202 is preferably transparent so as to allow a person wearinghelmet 200 to view their surroundings.

Armor plate 100 is particularly advantageous when used in articles thatare worn on the head of a person. The use of fracture layer 114 (FIGS. 8and 9) and armor plate 100 allows substantial percentages of themomentum of a bullet or other object to be absorbed into fracture layer114 without transferring momentum to be supporting structures such ashelmet structure 204. This protects the wearer from injuries that can becaused by rapid acceleration of helmet 200.

FIG. 12 illustrates yet another embodiment of a device that canincorporate armor plate 100. FIG. 12 shows goggles 220 having armorplate 100 e, which function as a lens. Armor plate 100 e is mounted inframe structure 222. Armor plate 100 e can be shaped to provide a lensfor correcting myopia and/or hyperopia. A strap to 24 allows goggles 220to be worn on a person's head.

While FIGS. 10-12 illustrate specific examples of devices in which armorplate 100 may be incorporated, those skilled in the art will recognizethat armor plate 100 may be incorporated into any structure where athin, armored, transparent and/or translucent plate is desirable. Forexample, armor plate 100 may be used in windows of buildings, panelingor walls in or on buildings, including buildings where target shootingis carried out. While the present invention is advantageous for use withdevices that need to be armored against artillery threats, the presentinvention is not limited to these. Armor plate 100 can be used in anyapplication where a projectile could pose a threat (e.g., motorcyclehelmets designed to protect against flying debris on a road).

In one embodiment armor plate 100 can be segmented into a panel of armorplates. FIG. 13 illustrates a panel 250 having four segmented armorplates 100 f. Segmented armor plates 100 f are mounted in a framestructure 252. Segmenting the armor plates reduces crack propagationbetween portions of the armor plate. In one embodiment, the individualsegments are sized to minimize crack propagation between segments whileproviding a suitable viewing area. Minimizing crack propagation preventsone segment from being compromised by a bullet striking an adjacentsegment. In one embodiment this segment can have a surface area in arange from about 1 cm² to about 30 cm² with about 3 cm² to about 10 cm²being more common. It is also appreciated that panel 250 can comprise awindow wherein each armor plate 100 f comprises window pane. The windowcan be mounted on a building or other type of stationary structure. Inthis context, each armor plate 100 f can have a much larger surfacearea. For example and not by limitation, the surface area of each armorplate 100 f can be in the range of 0.2 m² to about 2 m² with about 0.4m² to about 1 m² being more common. The window can also be limited toonly one armor plate 100 f or two or more armor plates 100 f.

Although the above examples primarily illustrate the inventive armorplates being used as transparent armor, it is also appreciated that thepresent inventive armor can be used in the same manner as conventionalarmor such as for body armor, helmets, and as panels on vehicles orbuildings. The inventive armor also need not be used in a militarycontext but can be used in any commercial product or in any contextwhere it is desired to provide protection or resistance against aprojectile of any form.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What we claim is:
 1. An armor plate comprising: a ceramic layer having afirst side and an opposing second side; and a fracture layer disposedadjacent to the second side of the ceramic layer, the fracture layerbeing comprised of glass and a plurality of particulate resonatorsdispersed within the glass, the particulate resonators having athickness in a range from 5 nm-100 microns, the particulate resonatorsbeing comprised of a material having a greater tensile strength than theglass.
 2. The armor plate as in claim 1, wherein the concentration ofthe particulate resonators in the glass is in a range from 0.001 vol %to 10 vol %.
 3. The armor plate as in claim 1, wherein the thickness ofat least a majority of the resonators is n*λ/2±λ/5 nm, where n is 1, 2,or 3 and λ is the wavelength of the phonons in the resonator.
 4. Thearmor plate as in claim 1, wherein the fracture layer is one selectedfrom the group consisting of glass, soda glass, a silicate material, anda combination thereof.
 5. The armor plate as in claim 1, wherein theceramic layer is comprised of one selected from the group consisting ofsapphire, aluminum oxynitride, spinel, AlN, alumina, silicon carbide,boronitride, boron carbide, diamond, and a combination thereof.
 6. Thearmor plate as in claim 1, wherein the resonators are comprised of oneselected from the group consisting of Al₂O₃, TiO₂, ZrO₂, MgO, AlN, TiN,ZrN, Si₃N₄, BN, SiC, TiC, WC, TiC, ZrC, TiB₂, and combinations thereof.7. The armor plate as in claim 1, wherein the armor plate istransparent.
 8. The armor plate as in claim 1, further comprising: adeformable layer disposed adjacent to a side of the ceramic layeropposite the fracture layer; and a spall liner disposed adjacent to aside of the fracture layer opposite the ceramic layer, the deformablelayer being comprised of a material having an elongation before breakingof at least 20%.
 9. The armor plate as recited in claim 8, wherein thedeformable layer has an elongation before breaking of at least 100%. 10.The armor plate as recited in claim 1, further comprising an adhesivejoining the ceramic layer and the fracture layer.
 11. A method formaking an armor plate, the method comprising: heating a fracturematerial to form a melt; dispersing a plurality of inorganic particulateresonators into the melt to form a fracture layer material, theparticulate resonators having a thickness in a range from 1 nm to 100microns and having a melting temperature higher than the meltingtemperature of the fracture material; and securing the fracture layermaterial to a ceramic layer.
 12. The method as in claim 11, wherein theconcentration of the particulate resonators in the melt is in a rangefrom 0.001 vol % to 10 vol %.
 13. A method as in claim 11, wherein thestep of securing the fracture layer comprises applying the fracturelayer material while in the state of a heated melt to the ceramicmaterial and then cooling the melt to form a solid fracture layer. 14.The method as in claim 11, wherein the step of securing the fracturelayer comprises cooling the fracture layer material to form a solid andthen applying the fracture layer material to the ceramic layer.
 15. Ahelmet comprising a helmet structure and a visor secured to the helmetstructure, the visor being comprised of the armor plate as recited inclaim 1, the armor plate being transparent.